A conventional float valve assembly stops water flow by means of a float valve, but the resisting disc of rubber in the valve has rather little resisting force against the water pressure when the water pressure is large. So it can hardly keep water from leaking in a water tower, and as the result the water in the water tower often overflows. Such a conventional float valve can get out of order quite easily, especially, if it cannot efficiently cope with a high water pressure, as its method of stopping water is against the water flowing direction.